POS0607 BREPOCITINIB PREVENTS TYPE-I INTERFERON INDUCED DAMAGE IN CULTURED MYOCYTES AND ENDOTHELIAL CELLS INDICATING A POTENTIAL ROLE IN THE TREATMENT OF DERMATOMYOSITIS
Authors: J. Vencovský, J. Feldman, L. Mcconnachie, B. Johnson
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Dermatomyositis (DM), an idiopathic inflammatory myopathy, is a chronic and often debilitating condition characterized by a hallmark skin rash (e.g., Gottron's sign and heliotrope rash) with perifascicular atrophy and subsequent muscle weakness <sup>[1]</sup>. The pathogenesis of DM involves dysregulation of Type I interferon (IFN-I) signalling and other cytokines (IFN-ɣ, IL-12, and IL-23). The kinases, TYK2 and JAK1, are essential for the signalling pathway of these cytokines. Brepocitinib, a selective and potent dual TYK2/JAK1 inhibitor is in development for the treatment of DM and is expected to reduce signalling of these cytokines, particularly IFN-I, and ameliorate the symptoms of disease. <h3>Objectives</h3> To evaluate the efficacy of brepocitinib in preventing IFN-I induced pathological changes characteristic of DM in human skeletal muscle and microvascular endothelial cells in vitro. <h3>Methods</h3> Human skeletal muscle myoblasts were cultured and differentiated into myotubes then treated with vehicle control or IFN-I (recombinant Human IFN alpha A and Human IFN alpha D) to induce cellular damage. Myotubes were also preincubated for 1 hour with brepocitinib (1 µM or 130 nM, the latter is equivalent to the average free plasma concentration after administration of 30 mg once-daily) prior to IFN-I treatment. Immunofluorescence staining followed by image analysis to determine myosin 4 surface area were conducted after 48 hours of IFN-I treatment. Human dermal microvascular endothelial cells (HMEC-1) were cultured and, once vascular networks were established, cells were treated with IFN-I or vehicle control. Cells were also preincubated for 1 hour with brepocitinib as described above. Under light microscopy 9 hours after treatment, the number of nodes, master segment length, and total mesh area were analyzed. To determine statistical significance, one-way ANOVA followed by Tukey's multiple comparison post-hoc analyses were performed. <h3>Results</h3> Myosin surface area was reduced by ~40%, relative to vehicle treated control, in myotubes exposed to IFN-I (p&lt;0.0001). This cytokine induced damage was almost completely prevented by brepocitinib preincubation (both 130 nM and 1 μM) with mean myosin surface areas of 96% and 100% of the vehicle control, respectively. The differences between IFN-I treatment alone and brepocitinib were significant (p&lt;0.0001 [1 µM] and P&lt;0.001 [130 nM]). Similarly, HMEC-1 exposure to IFN-I significantly reduced the mean number of nodes, mean master segment length, and mean total mesh area by 47 to 50% relative to vehicle control (p&lt;0.0001 nodes and segments, p&lt;0.001 mesh area). With brepocitinib preincubation, this damage was prevented with the mean number of nodes, master segment lengths, and total mesh area ranging from 89 to 111% of vehicle control. These differences were statistically different from the IFN-I treatment at both brepocitinib concentrations and all endpoints (p&lt;0.001 for all conditions). <h3>Conclusion</h3> One of the most debilitating aspects of DM is muscle weakness resulting from perifascicular atrophy leading to significant impacts on quality of life for these patients<sup>[2]</sup>. We report here the ability of brepocitinib to prevent IFN-I induced damage in both myocytes and microvasculature in culture at clinically relevant concentrations, providing further pharmacologic rationale for brepocitinib in the treatment of DM. <h3>References</h3> [1]Marvi, et al. <i>Indian J Dermatol</i> 2012;57(5):375-381. [2]Regardt, et al. <i>The Journal of Rheumatology</i> 2015;42(12):2492-2495. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Jiří Vencovský Speakers bureau: Abbvie, Biogen, Boehringer, Eli Lilly, Gilead, MSD, Novartis, Pfizer, Roche, Sanofi, UCB, Werfen, Consultant of: Abbvie, Argenx, Boehringer, Eli Lilly, Gilead, Octapharma, Pfizer, UCB, Grant/research support from: Abbvie, Jolie Feldman Shareholder of: Roivant Sciences, Employee of: Priovant Therapeutics, Lisa McConnachie Consultant of: Impel Pharmaceuticals, Employee of: Priovant Therapeutics, Brendan Johnson Shareholder of: Priovant Therapeutics, Roivant Sciences, Employee of: Priovant Therapeutics.